/* adler32.c -- compute the Adler-32 checksum of a data stream
 * Copyright (C) 1995-1998 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h 
 */

/* @(#) $Id$ */

#include "zlib.h"

#define BASE 65521L /* largest prime smaller than 65536 */
#define NMAX 5552
/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */

#define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
#define DO16(buf)   DO8(buf,0); DO8(buf,8);

/* ========================================================================= */
    uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len)
   {
      unsigned long s1 = adler & 0xffff;
      unsigned long s2 = (adler >> 16) & 0xffff;
      int k;
   
      if (buf == Z_NULL) 
         return 1L;
   
      while (len > 0) {
         k = len < NMAX ? len : NMAX;
         len -= k;
         while (k >= 16) {
            DO16(buf);
            buf += 16;
            k -= 16;
         }
         if (k != 0) 
            do {
               s1 += *buf++;
               s2 += s1;
            } while (--k);
         s1 %= BASE;
         s2 %= BASE;
      }
      return (s2 << 16) | s1;
   }
